dimanche 16 août 2015

Better NOT to (re)format a SD card ?



I just got a Samsung EVO+ microSD card. I was wondering if I should format it before using it. So I looked up the net on what was the best way to format a SD card. Came across many suggestions like use your smartphone, SD formatter, Windows format etc. Then I came across this :
http://wiki.laptop.org/go/How_to_Dam...Storage_Device


Quote:









To damage such a device, all you have to do is reformat it with any of the usual Linux-based tools like fdisk, mkfs, and dd. Chances are excellent that you will manage to choose a layout that makes the device work extra hard, thus slowing it down and wearing it out faster.
You can also accomplish the same feat using various Windows tools that are part of the Microsoft OEM Preinstallation Kit, and probably with other Windows-based tools (e.g. dd for Windows, and perhaps even with the GUI format capability).
...
Factory formatting.
The manufacturers of FLASH storage devices understand this. When they format the device at the factory, they know which filesystem they are putting on (typically either FAT16 or FAT32), the page and erase sizes for the NAND FLASH chips inside, and the characteristics of the FTL software in the internal microcontroller. (Actually, there is yet another factor - multiple NAND chips or multi-plane chips can further influence the locations of "efficient" boundaries.) Knowing this, they can choose a layout that encourages "easy case" internal operations.
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How to win.
It boils down to the fact that you need to micro-manage a lot of details to ensure that things fall on suitably-aligned boundaries. You need to consider both the partition map and the filesystem layout in concert. One way to separate the problems is to make each partition begin on an erase block boundary, then layout the filesystems so their subordinate data structures (particularly the cluster or "fs block" array) fall on erase block boundaries assuming that the partition itself begins erase-block-aligned. What is a good alignment boundary? Well, 256 KiB is good for most new chips, but to give some breathing room for the future, maybe 1 MiB would be better - or perhaps even 4 MiB.
Better yet, try to avoid reformatting FLASH-based devices when you have the choice.
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Bottom-line recommendations:
If you can, stick with the factory map
If you must make a "blast it on with dd" image, be very careful and conservative with the partition and filesystem layout, according to the techniques above.




What I intend doing is to make a (Symantec) Ghost image of the entire "disk" (the SD card) before I actually use it. This is done on Windows of course. The image preserves the geometry of the entire "disk". If I ever need to format the SD card, I will just restore this image to the SD card. This should result in a "factory formatted" card.

Many of you are more knowledgeable than me, please comment.



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